Mystery of lead-acid battery current solved

23-Feb-2012

Chemists have solved the 150-year-old mystery of what gives the
lead-acid battery, found under the hood of most cars, its unique ability
to deliver a surge of current.

Lead-acid batteries are able to deliver the very large currents needed
to start a car engine because of the exceptionally high electrical
conductivity of the battery anode material, lead dioxide. A team of
researchers have explained for the first time the fundamental reason for
the high conductivity of lead dioxide, reports ScienceDaily.

“The unique ability of lead acid batteries to deliver surge currents in
excess of 100 amps to turn over a starter motor in an automobile
depends critically on the fact that the lead dioxide, which stores the
chemical energy in the battery anode, has a very high electrical
conductivity, thus allowing large current to be drawn on demand,” said
Professor Russ Egdell of Oxford University’s Department of Chemistry, an
author of the paper. “However the origin of conductivity in lead oxide
has remained a matter of controversy. Other oxides with the same
structure, such as titanium dioxide, are electrical insulators.”

Through a combination of computational chemistry and neutron
diffraction, the team demonstrated lead dioxide is intrinsically an
insulator with a small electronic band gap, but invariably becomes
electron rich due to the loss of oxygen from the lattice, causing the
material to be transformed from an insulator into a metallic conductor.